All other things being equal, the faster you go, the more reactive the steering becomes (same angle but greater travelling distance at that angle), the more reactive you become, the more ...
After some years of Warrior riding I came across the wobble only recently. I put it down to a combination of the affects of track surface camber, track surface profile, corrugations and the natural tendency to self centre, only to be upset by the previous things. Mind you, I had taken both hands off to do something at the time. It was a gravel surface and speed was not great but was mildly scary for a second or so. Ordinarily, it doesn't happen.